1. Field of the Invention
The present invention relates to a cleaning apparatus for cleaning a workpiece that needs to have a high degree of cleanness, e.g., a semiconductor wafer, a glass substrate, a liquid crystal display, or the like.
2. Description of the Prior Art
As semiconductor devices become more highly integrated in recently years, circuit interconnections on semiconductor substrates become finer and distances between such circuit interconnections become smaller. When semiconductor wafers are processed, small particles such as particles of semiconductor material, dust particles, crystalline protrusive particles, or the like often tend to be attached to the semiconductor wafers being processed. If a particle greater than the distance between interconnections exists on a semiconductor substrate, then the particle will short-circuit interconnections on the semiconductor substrate. Therefore, any undesirable particles on a semiconductor substrate have to be sufficiently smaller than the distance between interconnections on the semiconductor substrate. Such a problem and a requirement hold true for the processing of other workpieces including a glass substrate to be used as a mask, a liquid crystal display, and so on. To meet the above requirement, there have been practiced some cleaning procedures for removing fine particles or submicron particles from semiconductor wafers.
For example, there has heretofore been one practice to use a brush of nylon, mohair or the like, or a sponge of polyvinyl alcohol (PVA) to scrub a surface of a semiconductor wafer. This process is called a scrubbing cleaning process. Further, there have been other practices, one of which is an ultrasonic cleaning process in which water having ultrasonic vibrational energy applied thereto is supplied to a surface of a semiconductor wafer, the another of which is a cavitation jet cleaning process in which high pressure water containing cavitation therein is supplied to a surface of a semiconductor wafer. Also, a cleaning process which combines two c)r three of the above processes is known in the art.
FIG. 4 of the accompanying drawings shows a known scrubbing cleaning apparatus for cleaning a semiconductor wafer. As shown in FIG. 4, the scrubbing cleaning apparatus has a plurality of vertical spindles (six in FIG. 4) 1 for supporting a circumferential edge of a circular semiconductor wafer W and rotating the semiconductor wafer W, a brush arm 2 disposed over the semiconductor wafer W and extending diametrically in one direction across and parallel to the semiconductor wafer W, a brush actuating mechanism 3 for vertically moving the brush arm 2 as indicated by the arrow G and rotating the brush arm 2 about its own axis as indicated by the arrow F, and a cleaning liquid nozzle 4 for supplying a cleaning liquid such as deionized water (pure water) to a surface to be cleaned of the semiconductor wafer W. The brush arm 2 has a brush on its entire cylindrical surface. The semiconductor wafer W has an orientation flat formed by cutting off a portion of its circular circumferential edge.
The spindles 1 are positioned at substantially equal intervals on a circle around the semiconductor wafer W. Since the brush arm 2 needs to be held in sliding contact with the entire surface of the semiconductor wafer W, the brush arm 2 has an axial length greater than the maximum dimension or diameter of the semiconductor wafer W. The brush arm 2 is arranged so as not to physically interfere with the spindles 1.
The semiconductor wafer W is supplied to the scrubbing cleaning apparatus from outside the scrubbing cleaning apparatus. A process of supplying the semiconductor wafer W to the scrubbing cleaning apparatus will be described below:
The spindles 1 are displaced away from the position shown in FIG. 4. In such a state, the semiconductor wafer W is fed by a robot hand 5 from a diametrically opposite position remote from the brush actuating mechanism 3 along the longitudinal axis of the brush arm 2 to a position over the spindles 1. The robot hand 5 has a substantially rectangular-shaped support portion 5a for supporting the semiconductor wafer W, and guide portions 5b, projecting from the supporting portion 5a for engaging with the outer peripheral edge of the semiconductor wafer W. The width of the support portion 5a is set to be smaller than the spacing between adjacent ones of the spindles 1. The rear end of the robot hand 5 is connected to a robot (not shown). The robot hand is then lowered to place the outer peripheral portion of the semiconductor wafer IV on the shoulders of holding portions of the spindles. and the spindles 1 are displaced inwardly to the position shown in FIG. 4 for holding the circumferential edge of the semiconductor wafer W by the holding portions of the spindles. Thereafter, the robot hand is further lowered and then moved back away from the scrubbing cleaning apparatus. While the semiconductor wafer W is being thus supplied, the brush arm 2 is retreated upwardly away from the spindles 1 by the brush actuating mechanism 3.
Thereafter, the brush actuating mechanism 3 is operated to lower the brush arm 2 toward the semiconductor water W until the brush arm 2 is brought into contact with the semiconductor wafer W. While a cleaning liquid is supplied from the cleaning liquid nozzle 4 to the surface of the semiconductor wafer W, the semiconductor wafer W and the brush arm 2 are rotated, thus cleaning the upper surface of the semiconductor wafer W. In FIG. 4, only the upper surface of the semiconductor wafer W is cleaned, however, another brush arm 2 may also be provided underneath the semiconductor wafer W so that both of the upper and lower surfaces of the semiconductor wafer W are cleaned simultaneously.
Because the spindles 1 are positioned at substantially equal intervals around the semiconductor wafer W, the spacing between adjacent ones of the spindles 1 is relatively small. The robot hand is moved in close proximity to the spindles 1, and the brush arm 2 is positioned relatively closely to the spindles 1. Therefore, the spindles 1, the robot hand, and the brush arm 2 need to be positioned such that they are kept out of physical contact with each other when the robot hand moves toward and away from the scrubbing cleaning apparatus.
It is difficult to position an additional brush arm underneath the semiconductor wafer W because the additional brush arm must be located between the spindles 1. Inasmuch as the robot hand needs to move between the spindles 1, it is not easy to determine a path along which the robot hand can move toward and away from the scrubbing cleaning apparatus. Designing the dimensions and path of the robot hand, the diameter and position of the brush arm 2, and the diameter of the spindles 1 suffers many limitations as the robot hand, the brush arm 2 and the spindles 1 must be kept out of physical contact with each other.
Further, since the spindles 1 are positioned at substantially equal intervals on a circle around the semiconductor wafer W, when the semiconductor wafer W is fed to the scrubbing cleaning apparatus, all of the spindles are not displaced so as to form equal clearance between the holding portions of the spindles and the semiconductor wafer W. To be more specific, in the conventional scrubbing cleaning apparatus, as shown in FIG. 5A, all of the spindles are positioned at 60.degree. intervals around a center C of the semiconductor wafer W to be supplied. The six spindles 11 are divided into two groups 11GR, 11GL, each comprising three spindles 11, which are independently driven by driving mechanisms, and the two groups 11GR, 11GL of the spindles 11 are displaced outwardly along a center line C.sub.L in opposite directions so that all of the spindles 11 are spaced from the semiconductor wafer W. Assuming that each of the groups 11GR, 11GL of the spindles 11 is displaced along the center line C.sub.L by a distance L, the spindle 11 positioned on the center line C.sub.L is also displaced by the distance L in a radial direction from the center C of the semiconductor wafer W to be supplied. However, the other two spindles 11 positioned apart from the center line C.sub.L are displaced by the distance L cos 60.degree. =0.5 L in a radial direction from the center C of the semiconductor wafer W to be supplied. In this case, if the distance L is too large, the shoulder of the spindle 11 cannot receive the outer peripheral portion of the semiconductor wafer W when the semiconductor wafer is lowered by the robot hand H. Thus, it is necessary to set the distance L to be within the width of the shoulder of the spindle. This means that a suitable clearance is required to properly transfer the semiconductor wafer to the spindles. However, since a suitable clearance between the holding portions of the spindles 11 and the semiconductor wafer W cannot be formed at the spindles 11 positioned apart from the center line C.sub.L, when positioning the semiconductor wafer among the spindles, there are some cases in which the circuniferantial edge of the semiconductor wafer contacts the top of the spindle 11.